As is well known, the common-mode rejection ratio (CMRR) of a differential amplifier (or other device) is a measure of common mode transient immunity. Specifically, CMRR is a measure of rejection by the device of unwanted input signals common to both input leads, relative to the wanted difference (communicated data) signal. An ideal differential amplifier would have infinite CMRR, meaning that the amplifier is able to analyze the received signal as if there were no unwanted signal present in the received signal. In general, infinite CMRR is not achievable in practice.
In certain instances, a respective communication system includes multiple circuits such as a transmitter and receiver that operate with respect to different ground potentials that vary greatly over time. In such an instance, providing common mode transient immunity is desirable because it ensures reliable transmission of data.